Variable condenser



c. N. EHRLICH 2,589,351

VARIABLE CONDENSER March 18, 1952 6 Sheets-Sheet 1 Filed Feb. 27, 1947 (i =YG MAX 1 //VV/V7WA TIM s m A away/145mm? no 3o 10 so 90.100 s %MOVEMENTOF SLIDE FORCURVEB y March 18, 1952 c. N. EHRLICH VARIABLE CONDENSER 6 Sheets-Sheet 2 Filed Feb. 27, 1947 March 18, 1952 c. N. EHRLICH VARIABLE CONDENSER 6 Sheets-Sheet 3 Filed Feb. 27, 1947 I FIGJT f if (37 J17 March 18, 1952 c. N. EHRLICH VARIABLE CONDENSER 6 Sheets-Sheet 4 Filed Feb. 27, 1947 W 7 w 5 V W Mar h 18, 1952 c. N. EHRLICH 2,589,351

VARIABLE CONDENSER Filed Feb. 27, 1947 6 Sheets-Sheet 5 Arm/mar c. N. EHRLICH 2,589,351

VARIABLE CONDENSER March 18, 1952 Filed Feb. 27, 1947 6 Sheets-Sheet 6 m FIG.Z9

Patented Mar. 18, 1952 UNITED STATES PATENT OFFICE The invention relates to a novel variable condenser of the type generally used for the tuning of resonant circuits in electronic apparatus.

The capacity of a condenser is determined by the active surface of the electrodes, the gap between the electrodes, and the dielectric constant of the medium filling the gap. By changing one or more of these three parameters, the capacity of a condenser-is changed. In variable condensers forindustrial use, means are provided to perform and control this change in a predetermined and repeatable way. It is desirable to prevent changes of any one of these three parameters due to mechanical influences in general, shock, vibration, or variations of ambient conditions, such as temperature, humidity, etc'., or at least tokeep such undesired changes as small as possible.

Knownvariable condensers mostly use complexmechanical structures to form the electrodes which are subject to dimensional changes under the above'mentioned influences. The relative'positionof the electrodes, and correspondingly their active surfaces and thegap between them, are controlled by mechanical arrangements of questionable rigimty.

As a result, most known variable condensers change their capacity considerably under the above mentioned stresses or variations of operating conditions, all of which are nearly always encountered under practical working conditions; Microphony, resulting from capacity fluctuations caused by mechanical vibration, is one of the most undesired of these changes. a

In order to keep these unwanted changes small, most knownvariable condensers have to be built with relatively large electrode surfaces and relatively large gaps between the electrodes. Large overall dimensions result, with long leads required to connect most known variable condensers with adjacent components of the circuit, and

instability due to stray coupling occurs. Furthermore, inductive components are thus introduced into the impedance of the condenser and, especially on higher frequencies, are not' negligible.

In order to overcome some of these difculties, variable condensers hav diums with a high dielel between the electrodes.

ides other defects, the field of application of these latter condensers is limited due to losses higher than those obtainable by using the best known dielectric material, i. e. air. 1

Other attempts have been made to solve these problems. For example, in U. Patent No.

Claims. (01. 175-415) 2,046,803, it has been proposed to construct a condenser comprising pairs of relatively movable rigid plates, which are moved toward and away from each other by cam arrangements. The plates remain parallel and, to accomplish this, a complex operating structure is provided. Thus, the reductionof unwanted variations effected by the use of rigid plates is seriously mitigated by the variations in capacity caused by effects on the operating structure controlling the gap between the electrodes. I

' Other variable condensers have been built comprising one rigid and one flexible plate. They have the advantage of small size relative to the maximum obtainable capacity and are of low cost. The flexible plate, being under constant stress deforms with time and changes of temperature, in turn causingundesired changes of capacity. Furthermore, it is impossible to obtain densers use specially cut plates, or separate padding condensers are provided in the circuit.

Last, but not least, the movement of the controls operating known variable condensers have limitations, which usually have to be overcome by drive mechanisms.

It is among the objects of this invention to provide an eiiicient, compact, and stable variable condenser; to provide such a condenser including rigid members, having electrically conductive surfaces constituting electrodes, 'and adjustably interrelated in an inherently structurally stable relation; to provide a variable condenser comprising hingedly interrelated rigid plates having electrically conductive surfaces forming condenser electrodes, including means defining the position of the hinge line therebetween and means for varying the opening between the plates to vary the condenser capacity; to provide such a condenser including means normally. urging the for varying the opening between the plates; to provide such a condenser in which one or more 7 of the plates may be provided with electrode areas of equal or' di'derent values; to provide a tuning unit including one or more of such condensers and a selector mechanism for conditioning said cam means for operation by a selected one of- Fig. 27 is a sectional view on the line 21-21 of Fig. 24 looking in the direction of the arrows, and showing the condenser operating mechanism in one position. v

Fig. 28 is a view similar to Fig. 27 showing the operating mechanism in its opposite position.

Fig. 29 is a perspective view of the inner plate of the unit shown in Figs. 24 through 28.

Fig. 30 is a perspective view of one of the outer plates of the unit.

Generally speaking, according to the present invention, a variable condenser is provided comthe operating means; to provide a unit including such condenser and trimmer condensers mounted therewith and having one electrode in common with one of the variable condenser electrodes; to provide such a condenser iiicluding a prising hingedly interrelated rigid plates having electrically conductive surfaces constitutingcondenser electrodes, and including means defining the hinge line between the plates and means for varying the capacity of the condenser.

slidemovable along one plate and a link pivotally interconnecting said slide and the other plate to control the opening between the plates to vary the capacity of the condenser; and in general to provide a variable condenser, electronic tuning unit which is novel, compact, inexpensive, Bfi'l'. cient and reliable under operating conditions. W

These, and other objects; advantages and novel features of the invention will be apparent from the following. description and the accompanying drawings.

In the drawings:

Figs. 1 through 3 are diagrams illustrating the theory of operation of the invention condenser.

Figs. land 5 .are sets of curves graphically setting forth the relation ,between factorsof the invention condenser. v v, j

Figs. 6 and 7 are front elevational and .side elevation views, respectively, of one embodiment which the condenser may assume in practice.

Figs. 8, 9 and 10 arev front elevation, side elevation, and bottom. plan views, respectively, of another practical embodiment of the invention.

Figs. 11,12 and 13 are views similar to Figs. 8, 9 and 10, respectively, of a further practical embodiment of the'invention. 1

Figs. 14 and 15 are perspective views of niultiple condensers embodying the principles of the invention. 1

Figs. 16 and 17 arev somewhat diagrammatic side elevation views of other embodiments of multiple condensers according to" the present invention.

Figs. 18 and 19 are side elevation views diagrammatically illustrating gangin arrangements for condensers embodyingth present invention.

Fig. 20 is a side elevation view diagrammatically illustrating a further embodiment of the invention.

Figs. 21 and 22 are perspective views illustrating two types of operating means for accurately varying, the capacity of a condenser constructed according to the invention, in a predetermined manner.

Fig. 23 is a perspective view of a selective elec-' tronic tuningunit incorporating a condenser according to the present invention.

Fig. 24 is a sectional elevation view, of a practical condenser construction embodying the invention, on the line E i-2 of Fig. 25,1ooking1i'n the direction of the arrows, with certain parts shown in elevation. I

Fig. 25 is a transverse sectional view on the line 25-25 of, Fig. 24 looking in the direc'tion of the arrows." V

Fig. 26 is a vertical sectional view on theline 26-26 of Fig. 24, looking, in the: direction of the ws J In,

The simplest condenser according to the present invention comprises a pair of rigid plates having electrically conductive surfaces forming the electrodes. The plates bear on each other at one end in a hinging relation, either directly or through the interposition of shims, or an insulating film. The operating means, which control the opening angle between the plates, are preferably located at the free or open ends of the plates, and preferably bear directly on the plates. As a result, a simple, structurally stable, rigid triangular structure is achieved, the plates forming two sides of the triangle and the third side of the triangle being formed by the operating means, which bear on the plates.

*Thus a basic structure for a variable condenser is obtained which is'rigid and stable undermechanical stress and variations of ambient con-' 'ditions. Capacity characteristics can be" obtioned, which follow a predetermined pattern within theclosest limits. Employing essentially air asmedium between the electrodes, losses are as low as governed by the quality ofthe dielectric used to insulate the electrodes The simple and rigid structure of the electrodes permits to keep their mechanical dimensions uniform in production and stable under working conditions. 'The means used to locate and space the electrodes against each other are of utmost rigidity. The invention condenser is based on the principle of hired active electrode surfaces and variable air gap between the electrodes. Thus the air gap increases with higher tuning frequencies.

The result is the possibility of using small electrode surfaces and small gaps forthe highest tuning capacity, withr'esultant small overall dimensions and low -inductive components in the overan" impedance of the variable condenser,

with microphony and similar defects greatly re duced, if not totally eliminated.

The possible arrangements to adjust the initial capacity simplify the task of uniform mass production with small tolerances, providing, in addition, for the attainment of any required padding effect in the simplest possible way. The movements of the controls operating the invention condenser are varied and can be made to suit the application.

The principles of operation will be understood best by reference to Figs. -1 through 5, which dia grammatically and graphically illustrate the the- I cry of the invention. Reference'to Fig. 1, which of the electrode planes from the hinge line -3-3-due v 6 to"separation of the plates by shims, insulating A, fllmsorthellkeii (5i F fi LR) Bydivlding theair gap of the condenser show-n LR in Fig? 1 into'three'parts'; the condenser-of Fig.- l I 1 I can be substituted electrically by the arrangea (-5) RDK(v-lcg.=L)- me'nt 'sh'o'wn in Fig. 2, which comprises two fixed G parallel pla'te condensers 'C" and C with eleci trode separations G2 and G3, respectively, (i7) (l-L)RDK -=RDK (-log.I-L} Series' with a -variable condenser C with a V-shapedgapandfa variable opening angle a. In in V L) most of the practical executions of the invention c condenser, the'fixed separations G2 and G: will bewery "I u furthermore formed by *As shown m Fig. 3. Gs is the gap between the mediums with a dielectric constant higher than ig s s v fi the edge m 9 th 1. Therefore, the capacity of the condensersC" 9 9 5 nim e the q and'C"'will be large compared'tothat of con- ?P t W keepingqs large as 993. denser 0: Knowledge of'the behavior of con-j 5 9 Wi m a with i i denser cf' alonewill therefore be conclusivefin 'fi i V 3? h a Pammeter- This may be mcisteasea for the behavior or thetotal capacity. "9 588d as Otherwise it is simple to reintroduce the-"effect of 20 (9) Gs=fLG the'series condensers by using 'the'formulafol-lowing relations when 11 1'1' 4.. g 7 IC CI+CII I C!!! Therefore.' in the followingmathemati'cal' treat i mentythe c pacity C, only-,zis analyzed, with v .(1-L)RD(-log,L) reference to Fig 3, whichshows this simplified G(1-L)' invention condenser diagrammatically. 1

In order to calculate the capacity of the unit (1.)) r: KR D of Fig, 3, a factor must be found which takes into consideration the inclination of theelectrode a .7 r surfaces wo 5 each other and the corresponding i ig g gim constant the following resmts changing-magnitude of theair-gap The -equa- [53M =Constant tion for the' capacity "of the condenser may be Gi=CD$ml1t 0 511 written as follows: I II I I I Ilia-Lord; LI'ILIwgIIIlI geei I 12L dL 3 ou I I. I I 1t I I :log, L-i'l-0I w, (1. 10g. L 1 A=Area of electrode surfaces I H V t Gequ=c1a of an" equivalent parallel plate condenser with the same electrode surface and qt n h be sjeenrtha; by having a m ea tm mately 37% of the total width of the plate in For a condenser with a V-shap'ed dielectric f G5 reajches maxlmum' 4th? e 4 curve for Z iepresents the relation of Gequ m gapbut having a very narrow electrode dz: the formulae 'for parallel plate condensers can be 377G with L as aparameter The curve of p Hows, -shows the relation of G; to G5 maxwith L as a ,1: parameter, wherein G's max sepresents tne value of I .GS of L=.368 (see Equation 17).;In-o1'der E f obta-in the maximum variationfin the capacity wherein "',0f thecondenser for a given vairiatiqn'of the air gap (G') it is advisableto use an inactive length (L) slightly higher than the optimum,- i. e.,

D 'DeIpth of electrode surfaces A=l('1=L)RD around 40%. This reduces the minimum vcapacdA=dxD ity of the condenser slightly while still keeping G's close to the optimum value. However, de-

'gi pending upon the particular application,- values R of L. from 30% to maybe usedw I I L=Percent of inactive width of R Fig. 5 shows th cap city variation with the I I gap G as a parameter; If the gap is varied G=Gap b w t es measure! Q h *4 linearly, the capacity decreases; very rapidly, as

edge farthest from hinge line i may be noted from the steep slopeof the curve A. e en e e s-m asu ed at e p051? Such a rapid initialchange in the condenser tion'dX I I 5 capacity in response to linear movement o f a R= t ce etee h nce lme nd e e s control is undesirable in practicer Accordingly, farthest" from 11 .2 86 1in? it is preferred to usea type of control-ill which i 7 v. V, r. the. variation of the gap is ncn-linearwith re} to a 1 1 For example, aslidingcam-mey have arcircu V, a y Ear -"ha ed surface ema ed b a cam follower. (a); w eni -mantis t i g y Gem 1; However, the same; efie'ct may-be time 4 using'a stationary circularcarn surface and a m ig tam toliq r m u d n i s A nati ly. G I the sarne jefiect-may be achieved by a slide movjslope than the curve AI, Curve B is based on using 45 of a circle as a useful cam using aalink' turning 45. a

The theory of the invention condenser having been set forth, the 'followingdescription will relate to possible. embodiments of the invention condenser. In this description, it should be borne in ii in marr e hzn ,.,i iu b s unitsfembo'dying the invention principles; in

surface or eluding details of various forms which the; plates may assume,f' a'nd various "arrangements for hingedly interrelating jthe plate s v through 20 illustrate various arrangements for forming multiple or ganged condensers embodying the invention, and means, for achieving pad?- ding efiects. Figs. 21 througlrfio illustrate means for varying the capacity of the condenser in a predetermined manner, vandfarrangements incorporating trimmer condensers. In particular, Figs; 24 through 30 illustrate a practical embodiment of the invention, comprising a fully enclosed, two-gang variable condenser for industrial "use.

As statedbasically the invention condenser comprises hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes, means defining the hinge line-with reference to these. ..plates, and means operative to vary the anglebetween the "plates to vary the capacity of the condenser. Fig's. 6.through l3 illustrate varied embodiments the plates them: selves may assume, and typical examples of means to define the hinge line. In these figures, the means to vary the angle between the plates are schematically indicated by'a link and will be described later in detail.

The rigid plates of the invention condenser maybe mace-or. dielectric material, or of metal, or of'combinatiohs thereof. Suitable dielectric materials are glass, ceramic, or the like. The electrically conductive surfaces on dielectric plates may be'formed bymetal' deposited by any known process, such as, for example, electroplating, metal-g sp'raying, or processes for depositing metal by h at or by chemical separation. Metal plates may have a homogeneous structure or may be formed 'by layers of-difi'erent metals, rolled together (if-otherwise joined permanently. They mayliave surface deposits of other metals, in "order to improve the electrical conductivity or the corrosion resistance of thefsurface, such as' for example brass plates with surfaces.

Composite plates may be formed by any known process, such as for example molded dielectric plates' withdnetal inserts,- or using composite plates, such as available in the tradefconsisting of dielectric sheets glued together with...met'al sheets.

withan insulating film or a film'to protectthe electrically conductive fsurfaoesor any other part of the plates against corrosion forhumidity, and thisf lm may be deposited a'nyknown process,

such as dipping, spraying, glueing or the like.

Th' film may serve the purpose insulation and silver-plated" V I The electrically conductive surfaces, or any other parts of the plates; may be covered,

stood that this is'by way of illustration only, -and that any one of the above mentionedexecutions of the rigid plates and conductive surfaces may be used many. one :ofl the: embodiments, if it is found practical forth'e particular'embodiment. Also, while the rigid plates are generally shown asY-bearing on" each other directly, it should be understood that, while this is a preferred execution, in any one of the embodiments, a shimora dielectric sheet maybe interposed between *the' plates.

Furthermore, wherever a dielectric plate with metal deposits forming electrodesis-described or shown, it should be understood that, in order tocompensate for the thickness of the metaldeposit of the-electrodes, a similar deposit maybe provided at the surface forming part of thehinge,-in order to achieve that the electrode planes; are situated in the hinge line, as shown diagrammatically in Fig. 3, and that these metal deposits may be electrically connectedw'ith the electrodes or may be insulated from them.

Additionally, while the drawings generally show:..both electrodes forming one capacity as being-.of the same size, in order to facilitate-the" description; in most practical executions the .hot electrode surface is smaller and is the. one which determines the active electrode surface and thus the capacity, whereas the cold electrode is larger, and acts preferably as an electrostatic shield. It is therefore understood, that this-shielding efiect may be provided in any one of the described embodiments, even if not shown in the drawing or particularly mentioned in=the description. :2

Also, the cooperative electrically conductive surfacesforming the electrodes of one capacity are always shown as facing each other. This is not done to limit the scope of the invention-to this particular execution but merelyto simpli'fy the illustrations. Wherever dielectric-"' material is'used'to form the rigid'plates, the electrically conductive surfaces of one or both plates'may be located on the other side of the plate? In such case, the dielectric material of oneor both plates becomes part of the mediumfillingthe gap between'the' electrodes. This may have advantages for certain executions of the condenser of the invention, such as, for example, for purposes of temperature compensation by using dielectric material to form the plates with the dielectric material having a defined temperature coefficient. Furthermore, it should be understood that though plates and electrodes are shown square as a preferred execution of theihyen-tio'n, they may take any suitable shape.

Figs. 6 and 7 show a typical embodiment of the condenser of the invention. Though any one or combinations of the above mentioned possible plate andielectrode executionscould be used, Figs. 6 and 7 show rigid plates 35 and 40 of dielectric material having metal deposits 36 and 31 forming electrodes. Lug terminals 38 and M are in electrical contact with the electrodes ihingedly interrelatedrelative to each other about a substantially fixed hinge'line 33', and are new in engagement by a U-shaped spring 43 having.

itsfree ends set-Lin recesses 44 and 46' of the plates.

Plates 35 and All are Shifting of the hinge line with relation to any one of the plates is controlled by forming each plate with a pair of aligned recesses 41 and 48 which jointly receive bearing balls 50. The recesses 41 in plate are formed with converging vre :t ilinear sides forming wedges pointing away from the hinge line. The remaining portion of the recess may have any shape as long as it clears the ball. In the illustration, it is circular. In plate 40, the right-hand recess 43 (Fig. 6 is'likewise formed witha wedge, but this wedge points toward the hinge line. The left-hand recess 48 has to have a shape to allow for manufacturing tolerances. In the illustration, it is substantially rectangular. The recesses have a depth at least equal to the radius of balls 59.

When balls 50 are engaged in the recesses and spring 43 is secured to the plates, the bight 3 of the spring bears against plate 40 and resiliently urges plate 35 toward the hinge line.

This .forces the balls into the wedge portions of recesses 4'! and Y48, causing the V-shaped edge of recess 41 to slide along the surface of ball 50 a counter-clockwise direction during opening of the condenser, and clockwise during closing. Thus, shifting of hinge line 33 along plate 40 'is effectively controlled or limited by such engagemerit of the recess edge and the ball surface. The shape of the recesses may be clearly seen in Figs. 29 and 30 which show perspective views of similar plates-with such recesses. In order to understand fully this locking arrangement, it should be borne in mind that, in practical "embodiments of the condenser, the angle between the plates never assumes a greater value than approximately 5.

Figs. 8, 9 and 10 show another embodiment of the invention. Though any one or combinations of the above mentioned possible executions for the plates and electrodes may be used, Figs. 8,

9 and 10 show a plate 45 of rigid dielectric material having ametal deposit 31 forming an electrode which is electrically connected to the terminal lug M. Two pins 52 are riveted to plate .5 and a terminal lug 42 is secured to the righthand pin (see Fig. 10). Plate '55 is made of metal and has one pin 57 secured to it. This plate is formed with an aperture to clear the head of lug 4| and with two recesses, one with a V-notch 5'3 and the other with a straight edge maintainingthe-position of the hinge line ,relatively to both plates.

. Though the angle between plates 45 and the outer edge. of plate 45 in order to prevent f hingeline 33 shifting too much relative to plate 4 5;for different opening angles of the embodime uf-i es de a r n s n al e i is :suilicient, for the purpose of the invention, that the hinge line isdefined for a certain open,-

ing angle of the unit, and it may assume another position for a different opening angle, as long as this shifting is controlled and retraced. The surface of the metal plate 55 acts as the second electrode of the condenser and, by means of pin 51, spring 53 and pin 52 is electrically connected to terminal lug 42. Thus spring 58 acts simultaneously as an electrical conductor.

Figs. ll, l2 and 13 illustrate another embodiment of the means to control the position of the hinge line relative to both plates, and also a special embodiment of a rigid plate. Here only plate 60 may assume any one of the above mentioned executions and en electrode may be provided for plate 33 according to any one of the above mentioned executions. In the illustrated embodiment plat-e68 is made of metal and serves as one electrode. leaf spring 62 is secured to plate Gil by means of two eyelets 6| one of which is provided with a terminal lug 64. Leaf spring 52'is likewise securedby eyelets 63 to a rigidplate 65 of dielectric material. Plate 65 is recessed, as at 39 and these recesses have a depth greater than the thickness of spring 62 so that the latter resiliently biases the plates into engagement at the hinge line 33 by the mounting tension.

Plate .65 is further recessed as at 66 and has eyelets" :67 secured near its outer edge, one of these having a terminal lug 68 secured to it. Plate"!!! is made of metal and serves as the other electrode. Two metal pins 59 are secured to plate ill. In order to provide, in such a composite plate, a predetermined relation between the surface which serves as an electrode and the hinge line, plates 55 and T0 are lined up, for example, in a jig, and then permanently joined by soldering pins 59 to eyelets 61. The'plates are held against shifting substantially parallel to each other by the lateral stiffness of leaf spring 62.

' Figs. 14 through 20 illustrate various arrangements of multiple or gang condensers embodying the invention, and also means to achieve padding eifects. The condenser arrangements shown in Figs. 14 through 30 use the plate constructions and hinge line controlling arrangements described in connection with Figs. 6 and 7. "This has been done to simplify the description, but should not be taken to limit these embodiments to these particular details. It should .be clearly understood that any of the condenser embodiments described hereinafter may incorporate any combination of the detailed arrangements or constructions described above.

.Fig. 14 shows a three gang condenser embodying the invention, but any plurality of capacities may be constructed in a similar manner. Alrigid dielectric plate 15 is provided with three electrically conductive surfaces ll forming electrodes. Two preferably grounded electrically conductive surface strips 12 shield the electrodes electrostatically from each other in a known manner. Plate may be made of metal, in which case its surface facing plate 15 constitutes the other electrode common to the three capacities, or it may be of dielectric material and have thesame arrangement of electrodes as plate 15. Means. defining the hinge line relative to plates 15 .and80 are the same as in Figs. 6 and '7, but only springs 13 are shown, corresponding to spring 43' of Figs. 6 and '7. Shields '12 may be omitted wherever shielding between juxtaposed capacities is not required. Themeans to .vary the capacity of the condenser are 'indicated schematically bya link 5!.

'11 Fig. 15 shows another embodiment of a multiple condenser according to the invention. As shown,

a rigid plate 85 has an electrically conductive surface I6 with shields I? connected to its mechanically andelectrically. Rigid plates 86, 81 and 88 of dielectric material have electrically conductive surfaces not visible in the illustration. Means defining'the hinge lines relative to the plates are I again'the same as in Figs. 6 and 7, and springs I8 correspond to spring 13. An arm 93 extends from plate'88 and has an adjustment screw 94 engaging plate 87. Similarly, an arm 9I secured to plate 8! is provided with an adjustment screw 92 engaging the plate 86, which has means to vary the capacity attached to it, represented schematically by'link 5I. The initial capacity of each unit can therefore be adjusted individually.

As the operating means indicated by link 5I are common, condenser elements with equal electrode arrangements'can be adjusted in such a way that they appear as having identical capacity characteristics, but with one or more of them being in series with a fixed condenser. Therefore, by simply adjusting the initial gaps to different values, any desired padding or series condenser 'efiect may be achieved.

ment by a U-shaped spring '83, which forms part of the hinge line control arrangement previously described. For purposes of illustration, the rigid plates are allshown as consisting of dielectric material having electrically conductive surfaces.

Fig. 16 illustrates another embodiment of a multiple .condenseraccording to the invention. Though shown here for two individual capacities, the same principle maybe applied to any desired plurality of capacities. .Plate 9i! has two electrically conductivesurfaces 95 and 98 which, co-

operating with electrode99 of plate 95, form two capacities C1 and .02. strip 91 maybe provided to act as an electrostatic shield as previously described. The condensers C1 and C2 can be dimensioned to have identical capacity curves, for example by keeping the values L and D, of Fig. 3 and the associated description, the same for condensers C1 and C2.

In Fig. 17, an arrangement is shown which is similar to Fig. 16. The only difference is that plate 95 is replaced by a plate I00. having its electrode surface stepped. Comparing the two figures, electrode H12 of condenser C2 has the same position with respect to electrode 98 as electrode 99 has in Fig. 16. However, electrode surface IOI is stepped back with the effect of an increased gap. Therefore, capacity C3 will have a characteristic equal to an arrangement of a condenser C1 in series with a parallel plate condenser of electrode surface 96 and gap equal to the step between surfaces I02 and IUI. Thus a padding effect is obtained.

Fig. 18 shows a pair of condensers, each identical'to that shown in Figs. 6 and 7, in which the plates 40 are schematically indicated as inter- Av preferably grounded v 12 connected by link 5I for gang operation. By adjusting the position of one plate 35, both pairs of plates may have the same opening angle, and thus the same capacity characteristic. Alternatively, and as indicated in the illustration, one pair may be adjusted to a variable opening angle a and the other pair of plates to the fixed angle [3 plus the same variable opening angle 11.. Thus again a series condenser effect may be achieved.

Fig. 19 shows a three gang condenser based on the same principle as the two gang condenser shown in Fig. 18, and including cooperating electrode pairs 35 and 3?.

Fig. 20 schematically shows another embodiment of the invention comprising three rigid plates I05, H and H shown, for example, as formed of dielectric material, held in engagement and controlled as to shifting of the hinge lines by arrangements as previously described and here indicated by spring 43. Inner plate H0 is provided with electrically conductive surfaces I06 and I0? forming electrodes on each face of plate III]. Outer plates I05 and H5 are formed with electrically conductive surfaces constituting electrodes I08 and I89 cooperative respectively with electrodes I06 and I57. Links 5| are schematically indicated as each connected to one of the plates I05, H5, illustrating suitable means, such as cams or the like, for swinging the outer plates with respect to the inner plates. Examples of such operating means are given hereinafter.

It should be understood further that the arrangements of Figs. 14 and may be combined to form multiple condensers, as for example by r providing two plates 85 of Fig. 14 on each side of plate I5 in order to combine the principle of this arrangement with that of Fig. 20. y Having described basic embodiments of the invention condenser, means for varying the condenser opening angle will now be described with tween the plates would change and herewith the capacity; This arrangement is very often used for-adjustable condensers, like trimmers. The capacity characteristic of such an arrangement I would follow a curve corresponding to curve A of Fig. 5, the screw changing the gap in linear rela tion to its rotation. In order to shape the characteristic to suit applications like tuning COD-{- densers in radio receivers, curve A would be un-fsuitable. By replacing the above mentioned screw with one with variable pitch, more specifi cally referred to in the art as a hight cam, any desired characteristic can be obtained.

Fig. 21 shows an arrangement using a rotary radial cam, an embodiment which would be more suitable for production purposes than a hight cam. As shown, the condenser in this instance likewise comprises a pair of rigid plates I20 and.

I25, hingedly interconnected and controlled as to shifting of the hinge line by means as shown in Figs. 6 and 7 and here illustrated by spring 43. In the particular arrangement shown, plate I25 is shown as made of dielectric material having electrically conductive surfaces IIS and 8 constituting electrodes and a strip II'I which may serve as an electrostatic shield as previously described. Plate I20 has metal pins I24, I24 secured to it.

A shaft I2I is rotatably mounted in any suitable position on plate I25, being illustrated, for

will adjust the opening between the plates and Y thus vary the capacity of the condenser. In order accurately to set cam follower I23 with respect to a fixed point on cam I22 and to adjust the capacity to the predetermined value of this cam position, cam follower I23 is preferably soldered V to pins I24 and thus fastened rigidly to plate I20. This permits setting of the parts in their predetermined position in an easy and accurate way, for example by means of a jig, and holding them there while performing the above mentioned se curing operation.

Fig. 22 illustrates another arrangement for varying the capacity of the condenser by cam means. Plate I35 has electrically conductive surfaces I26 and I28 constituting electrodes and an electrostatic'shield I21 may be provided as previously described. A slide I34 is movable along plate I35 and guided by a groove I36. Slide I34 may have an indicator I31 fastened to it, which cooperates with a scale I33. The slide operating means comprises a cord or cable- I4I engaging a grooved control shaft I42 and extendingaround a pulley I43. A second rigid plate I30 is'shaped to form a cam surface I3I. Plates I30 and I35 are held in hinging relation with means similar to those of Figs. 6 and 7, represented here by spring 43.

Secured to slide I34" is a cam follower I33 engaging cam surface I3I. Rotation ofshaft I42 moves the slide, changing the separation of the plates and thus the capacity of the unit. As previously described, the cam follower may be secured to the slide by means of soldering in'order to have cam follower I33 engage cam I 3I at a 14 part of a circle, and the second means being a rotary cam which operates the first cam.

With reference to Fig. 22, and using this principle therein, the cam surface I3I would be part of a circle, and slide I34 would be operated by a rotary cam. The requirements for this rotary earn from the point of view of precision are not very high due to the fact that'cam I3I and slide I34 magnify the movement of plates I and I35 relative to each other to such an extent that, for example, in one. typical practical embodiment,lslide I34 moves on the high capacity end of the characteristic; that is, for close spacing of the electrodes, one hundred times fasterthan the platesmove against each other. This means that, for example, a tolerance requirementof plus or minus" .0001 inch on the spacing of the electrodes could be met by a tolerance of plus or minus .01 inch on the rotary cam.

The same effect can be achieved with a cam follower fastened to one plate and the circular cam being part of the slide. Such an execution is shown in Fig. In order to keep the men:

. ber of figures at a minimum, the embodiment of predetermined point for a predetermined position of slide I34, and to set the capacity forthis slide position to a predetermined value.

In order to obtain capacity characteristics within usable tolerances, cam I22 of Fig- 21 and for example, cam surface I3I in Fig. 22 form part of a circle. This would change the grinding operation from a shape grinding to a standard internal grinding operation. Assuming, for example, that cam I3I in Fig. 22 forms a 45 are or A; ofa full circle, the capacity curve would: follow curve B, of Fig. 5. This brings the slide travel and the separation of the plates into a fixed relation which is not always acceptable in practical executions.

By introducing another nonlinear means, a mechanism is obtained which might look complicated but in practice is simple and offers valuable fiexibility in designing means to operate the condenser to suit the application. Therefore, onepf the preferred embodiments of the operating means of the condenser of the invention uses two nonlinear means in series with each other, the first means, which acts directly on the plates, being a cam with a surface which is Fig. 23 incorporatesat the same time other'features; of the invention. Fig. 23 illustrates' how the invention condenser may be incorporatedinto a complete selective tuning unit of the type, for example, whereby a radio set may be selectively operated on any one of a number of preselected wave bands. Such units may be used, for instance, to preset a radio receiver'for operation either on the standard broadcast band or on'the short-wave band. The arrangement shown in Fig. 23 is typical only'of the principles involved and may assume other forms in practice.

vAs shown, it comprises a condenser formed of rigid plates I40 and I which may be any of the types previously'described'. Plate H0 is illustrated as having a U-shape. Plate I 45 isillustrated as having electrically conductive sue faces "I46 and I48 which cooperate with surfaces ofplate 'I40 to form variable capacities. Strip' I41 may act as an electrostatic shield as previously described. A "pair of U-shaped springs- 43, 43 maintain the plates in hinging relation and help to control shifting of the hinge line, also as previously described. Plate I40 is provided with a cam follower I5 I, secured thereto by solderirig for initial adjustment purposes as describedin connection with Fig. 21.

Plate I 45 is formed with a surface I52 having a groove I53. A slide I is movable along the surface I52, havingfia tongue fitting in groove I53. Slide 255 is formed with two cam surfaces I56 and I51, differingin profile. An upper guide I54 fastened to plate I45 or any pertinent part maintains slide I55 against surface I52 and has" anap'er'ture I68 through which follower I5Ipro- J'ectsto engage cam surfaces I56 or I51.

Mounted adjacent either end of the path of movement of slide I55 are a pair of rotatable cams I58 and I59 which are secured to shafts, acting or being connected with tuning controls. Slide I55 is biased intoengagement with either of cams I58 or I59 by rotation of a selector shaft I60 having an arm I6I connected by springs I 02,

operated by cam I59. If shaft I60 is rotated in the opposite direction arm I6I assumes a poSia a ram tion centered around I32 and slide I 55 is biased to the-left, wherein it is operated ;by cam-. I58 and cam follower II engages cam. surface I51.

Cam :58 might be, for example, connected with ition comprises a circular camand a-ca-m fol- "lower on a slide or acam follower cooperating "with a circular -cam which forms part of a slide. Ineither one of these two preferred solutions the genes was operated by a rotary cam. The same {-jaction, andthus the attainment of a capacity curve B of Fig. 5' relative; to. the movementof ythe-slide, can be obtained by connecting-the slide by means of a link with the movableplate. Such Ifan execution is shown in Figs g24 -through 30 i-illustrating a typical industrial embodiment of a two gang variable; condenser accordinghto'lthe invention. This embodiment shows a typical fixa liample of how trimmers are incorporated ,jv-ith the condenser of the invention and how other problems of theprior art are solved.

schematic way in Fig-.- 20. In the embodiment i shown, the threeplates I15, I80 and I85 i are v Ifmade of rigid dielectric material. Side platefIBS, which is a mirror copy of side plate I15, isshown in-Fig. 30 as comprising a generally rectangular portion Int-joined byareduced portion I13 to a cross arm lld, which has edges 2 33, 233 which form the hinge-line-o'f this plate. The surfaces of portion ,I12 and arm I14 are ground to;be i -perf fectly flat with relation to each other. The electrode'is formed by a metal coating I16, and; the ,"fsame coating is applied to surfaces 218,218, to

maintain the ground flatness. 3 continued over a beveled surface I11 in order to connect electrically with a metal coatedsurface I18, which acts as terminal strip for. theelectrode as will be described later. Coating? I16 being the electrode which determines the 's'ize of the active electrode surface of the condenser, it

is important to keep its dimensions accurate. It can be readily understood that the edges of'coating.I18..c an be ground v.tosize, without injuring th' jc'onnection to surface 118. The outerv edge of plate I85 has a round, countersunk and ground recess I8I fora purpose to be described later.

' Additionally, arm I14 provided withre- ;geesses I82, 182; corresponding to recesses fl of plate 35 .in- Figs- 6 and 7, and having a function as described for. those. a

. Plate I80 is shown in Fig. 29 as beinggenerally rectangularfand formed with surface recesses I83. Both surfaces of plate I 8.0 are ground fiatiand metal coat-ed as indicatedat I84. These metal coated electrically conductive surfaces are larger than the electrodes I18 of plates I15 and 5.85,. and their si'zetherebydoes not determine the size of the active electrode surfaces of. the condenser. The metal coating I84 extends into the recessesl83 for the purpose of forming an electrostatic shield between the two capacities tithe condenser- .Thefrqnt e ge qrplate I80 lnflEigs. 24 through 30 the plate and electrode arrangement is the same as illustrated in a more.

Coating I18 is' is formed with a ground V-shaped groove I86 and near the rear edge recesses I81, I81 are provided corresponding with recesses 08, 48 of plate 40 in Figs. 6 and 7. Recesses I81, I81, -cooperate with recesses I82, I82 of plates-I15 and I85 to receive balls I88, I88 which act to control shifting movement of the hinge line-as previously described in connection with Figsnfi and 7. A U-shaped spring 589- resting with its center bend against plate I80 and with its free. ends engaging shallow grooves I90 of plates I15 and I85, maintains the three plates in assembled relation, and assists in controlling shifting of-the hinge line in the same manner as previously described.

A chassis I1I is provided, having a bushing I92 staked to it. A shaft HSI extends through the bushing I92, having on one side a cam I secured to it, and the other end I93 of the shaft serves as control to operate the condenser. A stop pin I91 on cam I95 is arranged to engage either of a pair of fixed abutments I98; I98 to limit rotation of the cam to 270.

The chassis I1I extends to the back of the assembly, where it is formed with-ears' 23l, 23L Plate I80 is secured to these-ears by means of eyelets 232 232, and blocked against play in the chassis near the forward edge by dimples 2 34, 234 of the chassis I1 I. In order to hold plate I80 centered and located with respect to shaft I 9I, a ball I94 engages in groove I88 of plate I80, and in a countersink of shaft .I9I. Balls I98 counteract the axial thrust and eliminate anyplay in the bearing. arrangement of 0am I95.

Cam I95 cooperates with a cam follower 2I2 secured to a slide 200. This slide includes a flat portion 20I extending transversely of the free edges of the condenser plates, and cylindrical extrusions receiving balls 202 riding along groove I86. The slideis provided at either end with upturned ears 203, 204 and strips 205 and. 206 extend between each pair of cars and are secured to the cars by soldering as will be explained later. Thesestrips have holes receivr ing balls 201,201 which engage corresponding holes in links 208, 208. The other ends of these links have holes receiving balls 2I0, 2I0 which set in the previously described countersinks I8I in the free edges of plates I15 and I95. A U- shaped wire spring 2I I extends around the plates, havingits bight engaging plate I80 and its free ends secured to links 208. The spring tends to pull the links 208, 208 towardmthe plates and presses balls 2I0 and 201 into their seats. Balls 201 press balls 202, 202 into thefgroove I86 of plate I80 by means of the strips 205, 20B Iand slide 200; This way the whole-fmechanism is held under tension and all bearing play is eliminated. 'During'assembly, the ends of spring 2 receive a torsional mounting tension, which tends to rotate the links 208, 208 in-such a way that the slide presses cam follower 2I2 against cam I95. Round pads 235 of dielectric material hold slide surface 200 spaced from chassis I1I.

As cam I95 is rotated, the previously described tension of spring 2 holds cam follower 2I2 in engagement with the cam surface. The slide moves along'groove I86, and by means of links 288, 208 operates plates I15 and I85, thus varying the opening angle between the plates and the capacity of the condenser. Fig. 2'1 show the mechanism positioned in such a way thaf'the plates assume their largest spacing, i. e. the condenser reaches its minimum capacity. Fig. 28

shows the mechanism in what may be termed the initial position, with links 208, 208 perpendicular to the slide travel and with plates at minimum spacing and therefore the condenser in maximum capacity position.

In order to adjust the condenser, th cam is brought to this initial position, and the cam follower held in engagement with the cam surface. Links 2&8, 2E3 are held by a jig in order to make sure that they are perfectly perpendicular to the plate I89, as viewed in Fig. 28. By moving the links toward or away from plate I60 the distances between the center. plate and each outer plate can be set individually and thus the two capacities of the condenser. When this is accomplished, strips 205 and 236 are soldered to ears 283 and 2-34 of the slide, as indicated at 238, 231, respectively, in order to set the mechanism permanently to this predetermined relation. By rotating shaft I the condenser will assume a predetermined capacity relative to each shaft position. As plates I15 and i8 5 have individual means Of adjustment, the two capacities of the condenser can be set to have any desired padding effect relative to each other, as previously described with particular references to Fig. 18. By using different metals for the links 288 and slide Eel, the temperature coefficient of the condenser can be adjusted to an extremely small value.

Trimmer condensers are mounted between the center plate and each of the outer plates. The electrically conductive surfaces I 84 of plate I 85 are used as one electrode of" the trimmer condensers. The second electrode is formed by parts 2I4 made of spring metal, and clamped between insulating washers 2I5, 2I6 by means of a rivet 2H, and thus secured in their location at the lower end relative to plate Hi0. Each spring 2I4 has a center tongue 226 struck out therefrom, which is secured by a rivet 22I to plates I15 and I85 respectively and thus in electrically conductive engagement with the terminal strips Ill, of electrodes H6. As can be seen, the upper part of spring 2'I4 is independent of tongue 220 in its movement toward and away from plate I83.

Threaded bushings 223, 223, are secured to chassis Ill and screws 222, 222 of dielectric material are inserted, with their bullet-shaped ends engaging lips 224 of springs 2I4. The springs 2 I4 have a tendency to move away from plate I80. By moving screws 222 down, lips 224, and thus springs 2I4 are forced toward plate I80, increasing the capacity between the electrically conductive surfaces I84 of plate I80 and springs 2I4. The latter are in electrical contact with electrodes I15, forming therewith trimmer condensers, serving known purposes. By providing the previously mentioned recesses I83 in plate I80, the clearance for spring 2I4 is increased and thus the minimum capacity of the entire condenser reduced. In order to prevent short circuits between the electrodes facing each other, the conductive surfaces I84 of plate I80 are covered with an insulating coating. This coating has to be removed under the lower ears 23I of chassis [H in order to obtain an electrically conductive connection between surface I84 and chassis "I.

The above described chassis assembly, with capacities adjusted as described is mounted in a housing I10, having a somewhat T-shaped form and being made preferably of sheet metal, to obtain a shielding effect. It is a preferred execution to solder chassis I1I to housing I10. Bushings 239 of dielectric material having eyelets with lugs 2I9 secured to it, are threaded from outside into chassis HI and somewhat L-shaped shields 2 I3 are secured between bushings 239 and housing I10. These shields serve as ground connections and at the same time shield lugs 2I9, 2I9 from each other. In order to finish the assembly, lugs 2i?) are soldered to the springs 224 at 2I8. Three spade bolts 238 are secured to housing I 10 and serve as mounting means for the condenser.

The described construction provides a novel variable condenser unit in a compact form including associated trimmer condensers, having one electrode in common with one main variable condenser electrode. The operation of the condenser is easily effected by rotation of the shaft extension 93.

The condensers constructed according to the present invention have the advantage of stability, reliability and compactness. Capacity variations due to mechanical stress and changes of ambient conditions are reduced to a minimum by the use of rigid plates arranged in a structurally stable triangular relation. Close tolerancescan be kept on the capacity curves, and thus high precision condensers built. compactness is achieved by the ability to use very small initial plateseparations and due to the required small relative movements of the plates.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles thereof, it should be understood that such illustrations are exemplary and that the invention may be otherwise embodied without departing from such principles.

What is claimed is:

1. A variable condenser comprising, in combination, hingedly interrelated rigid plates bearing on each other along a hinge line; said plates having electrically conductive surfaces forming electrodes; means disposed between and interengaged with facing surfaces of said plate adjacent the hinge line and limiting substantially parallel relative movement of said plates to control shifting of the hinge line relative to said plates; at least one of said electrically conductive surfaces being substantially rectangular, with one side thereof parallel to the hinge line, the width of said one conductive surface, measured along a perpendicular to the hinge line, being from onehalf to twice the distance between the hinge line and the nearest side of said one conductive surface; and means operative to vary the angle between said plates to vary the capacity of the condenser.

2. A variable condenser comprising, in combination, hingedly interrelated rigid plates bearing on each other along a hinge line; said plates having electrically conductive surfaces forming electrodes; means disposed between and inter-engaged with facing surfaces of said plate adjacent the hinge line and limiting substantially parallel relative movement of said plates to control shifting of the hinge line relative to said plates; and means operative to vary the angle between said plates to vary the capacity of the condenser; at least one of said plates having a plurality of conductive surfaces spaced from each other in a direction parallel to the hinge line, each constituting an electrode and each cooperative with a conductive surface on another plate to constitute a plurality of individual capacities; the inner edges of said spaced conductive surfaces being spaced substantially from the hinge line in a direction perpendicular to the latter.

3. A variable condenser comprising, in combination, a first rigid plate; a plurality of second rigid plates each hingedly interrelated with said first plate; said plates each having electrically conductive surfaces forming electrodes; means defining the position of the hinge line relative to said plates; and means individually operative to adjust the initial angle of each second plate to said first plate, whereby each of said second plates may have an initial adjustment differing from the other second plates; and means operative to vary the angle between said plates to vary the capacity of the condenser.

4. A variable condenser comprising, in combination hingedly interrelated rigid plates said plates having electrically conductive surfaces forming electrodes; means defining the position of the hinge line relative to said plates; and means operative to vary the angle between said plates to vary the capacity of the condenser; at least one of said plates having a recess facing another plate, and a trimmer condenser mounted in said recess having one of its electrodes constituted by a conductive surface of one of said plates.

5. A variable condenser comprising, in combination, a pair of hingedly interrelated rigid plates bearing on each other along a hinge line; said'plates having electricallv conductive facing surfaces forming electrodes; the electrodes of one plate being coplanar and those of the other plate being stepped; means disposed between and interengaged with facing surfaces of said plate adjacent the hinge line and limiting substantially parallel relative movement of said plates to control shifting of the hinge line relative to said plates; and means operative to vary the angle between said plates to vary the capacity of the condenser.

6. In a variable condenser of the type comprising a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes and means operative to vary the angle between the plates to vary the capacity of the condenser; means controlling shifting of the hinge line relative to said plates, said means comprising facing recesses in the juxtaposed surfaces of said plates and a ball in each facing pair of recesses, at least one recess of each pair intersecting a plate surface in a sharp edge riding on the surface of the ball during hinging movement of said plates, the sharp edges of said recesses being V-shaped in the plane of the surface; and resilient means biasing said plates toward each other substantially at the hinge line and in opposite directions parallel to said surfaces to maintain such sharp edges bearing on said balls to loclfthe plates against uncontrolled relative sliding movement.

a: 7 In a variable condenser of the type including 'a"'p'ali r of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes andmeans' operative to vary the angle between the plates to vary the capacity of the condenser; a hinge line shifting control arrangement comprising a pair of grooved pins secured in projecting relation to one plate, the other plate being recessed on an edge to rest on said pins; athird grooved pin secured in projecting relation to the other plate; and a spring engaged in the grooves of said pair of pins on the sides of the latter spaced from said recessed plate edge and in the groove of the third pin inwardly of such recessed plate edge, said spring engaging the outer surface of such other plate, to bias the plates toward each other and the other plate toward said pair of pins to control shifting of the hinge line relative to the plates.

8. In a variable condenser of the type including a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes and means defining the position of the hinge line relative to the plates; mechanism operative to vary the angle between the plates to vary the capacity of the condenser, said mechanism comprising a cam surface extending longitudinally along the inner surface of one plate; a member slidably mounted on the inner surface of the other plate for movement therealong in longitudinal alignment with said cam surface; and a cam follower secured to said member for engagement with said cam surface; the connection of said cam follower to said member being made by soldering to provide for accurate setting of the initial opening angle of the plates.

9. In a variable condenser of the type including a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes and means defining the position of the hinge line relative to the plates; mechanism operative to vary the angle between the plates to vary the capacity of the condenser, said mechanism comprising a cam follower arranged to be secured to one plate; and a slide movably mounted on the other plate and having a cam surface continuously engaged by said cam follower; the connection of said cam follower to said one plate being made by soldering to provide .for accurate setting of the initial opening angle of the plates.

10. In a variable condenser of the type including a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming slide will vary the opening angle of said plates;

a plurality of cam means mounted on said one plate and each selectively engageable with said' slide to move the same to align a diiferent one of said cam surfaces with said cam follower; and

means connected to said slide and said one plate and selectively operable to bias said slide into engagement with a selected cam means to engage said follower with a selected cam surface; the connection of said cam follower to said other plate being made by soldering to provide for accurate setting of the initial opening angle of the plates.

11. In a variable condenser of the type including a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes and means defining the position of the hinge line relative to the plates; mechanism operative to vary the angle between the plates to vary the capacity of the condenser, said mechanism comprising a slide mounted for sliding movement along one plate and having a plurality of cam surfaces differing in profile; a cam follower secured to the other plate and engaging said cam surfaces, whereby movement of said slide will vary the opening angle of said plates; a pair of cam means mounted on said one plate at either end of the path of movement of said slide and each selectively engageable with said slide to move the same to align a different one of said cam surfaces with said cam follower; and means connected to said slide and said one plate and selectively operable to bias said slide into engagement with a selected cam means to engage said follower with a selected cam surface; the connection of said cam follower to said other plate being made by soldering to provide for accurate setting of the initial opening angle of the plates.

12. In a variable condenser of the type including a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes and means defining the position of the hinge line relative to the plates; mechanism operative to vary the angle between the plates slide to move the same to align a different one of follower with a selected cam surface; the connection of said cam follower to said other plate being made by soldering to provide for accurate setting of the initial opening angle of the plates.

13. In a variable condenser of the type comprising three hingedly interrelated rigid plates, including an inner plate having electrically conductive surfaces forming electrodes and a pair of outer plates each having an electrically conductive surface forming an electrode cooperative with an inner plate electrode,.and means defining the position of the hinge line relative to the plates; mechanism operative to vary the angle between the plates to vary the capacity of the condenser, said mechanism comprising a casing enclosing said plates and having a wall adjacent the free edges thereof; a groove along the free edge of the inner plate; a cam rotatably mounted on said wall on an axis perpendicular to such free edge on the inner plate and having rotary bearing engagement in such groove to fix the inner plate against swinging movement relative to said cam; a slide movably mounted on the free edge of said inner plate for movement along such groove; a pair of links each pivotally connected to said slide and each pivotally connected to an outer plate; and means connected to said plates and slide and biasing said slide into engagement with said cam for movement thereby along the groove to operate said links to swing the outer plates relative to the inner plate.

14. In a variable condenser of the type comprising three hingedly interrelated rigid plates, including an inner plate having electrically conductive surfaces forming electrodes and a pair of outer plates each having an electrically conductive surface forming an electrode cooperative with an inner plate electrode, and means defining the position of the hinge line relative to the plates; mechanism operative to vary the angle between the plates to vary the capacity of the condenser, said mechanism comprising a casing enclosing said plates and having a wall adjacent the free edges thereof; a groove along the free edge of the inner plate; a cam rotatably mounted on said wall on an axis perpendicular to such free edge of the inner plate and having rotary bearing engagement in such groove to fix the inner plate against swinging movement relative to said cam; a slide movably mounted on the free edge of said inner plate for movement along such groove; relatively rigid means pivotally secured to said slide and the outer plates; and means biasing said slide into engagement with said cam for movement thereby along the groove to operate said relatively rigid means to swing the outer plates relative to the inner plate.

15. In a variable condenser of the type including a pair of hingedly interrelated rigid plates having electrically conductive surfaces forming electrodes and means defining the position of the hinge line relative to the plates; mechanism 0perative to vary the angle between the plates to vary the capacity of the condenser, said mechanism comprising a slide mounted for sliding movement along one plate; and a link pivotally connected to said slide and pivotally connected to another plate; the connection of said link to at least one of the elements it interconnects being made by soldering to provide for accurate setting of the initial capacity of the condenser.

CHARLES N. EHRLICH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,520,329 Cherpeck Dec. 23, 1924 1,538,472 Crosley May 19, 1925 1,698,190 Fredrlckson Jan. 8, 1929 1,735,532 Dubilier Nov. 12, 1929 2,210,029 Egerland Aug. 6, 1940 2,429,085 Albin Oct. 14, 1947 2,474,988 Sargrove July 5, 1949 2,476,930 Towle July 19, 1949 FOREIGN PATENTS Number Country Date 27,257 France Jan. 29, 1924 542,364 Germany Jan. 23, 1932 

